This invention relates to a magnetic head, and a magnetic head and a magneto-optical disc recording device used for recording on a recording medium. Particularly, this invention relates to a magnetic head for supplying a magnetic field when recording an information signal onto a recording medium, and a magnetic head and a magneto-optical disc recording device used for recording on a recording medium.
There have been used magnetic recording media such as a magnetic disk and a magnetic tape on which an information signal is magnetically recorded and reproduced, and magneto-optical recording media such as a magneto-optical disc on which an information signal is recorded and reproduced by using the magneto-optical effect of a recording film.
On a magnetic recording medium such as a magnetic disk or a magnetic tape, an external magnetic field is applied to change the local direction of magnetization of the magnetic recording medium by using a magnetic head, thus writing an information signal.
On the other hand, on a magneto-optical recording medium such as a magneto-optical disc, while a condensed laser beam is cast onto a recording film, an external vertical magnetic field modulated in accordance with an information signal is applied by using a magnetic head to a portion which is locally heated to the Curie temperature or higher, thus writing the information signal. That is, in the portion heated to the Curie temperature or higher of the recording film of the recording medium, the coercive force is lost and the direction of magnetization is changed in accordance with the external magnetic field. On the magneto-optical recording medium, a laser beam which is weaker than in recording is cast onto the recording film and the rotation of the plane of polarization of the laser beam corresponding to the direction of magnetization due to a Kerr effect is detected, thus reading out the information signal.
An example of the magnetic head used for the magneto-optical recording medium will now be described with reference to FIG. 1. A magnetic head 200 shown in FIG. 1 has a magnetic core member 202 on which a coil 201 for magnetic modulation is wound. The magnetic core member 202 is made of a material having a high magnetic permeability and has a substantially prism-shaped base 203, substantially prism-shaped yokes 204a, 204b provided to protrude upward from both ends of the base 203, and a substantially prism-shaped magnetic core 205 provided to stand upward from the base 203 at a position between the yokes 204a, 204b, as shown in FIG. 2. On outer circumferential surface of the magnetic core 205 of the magnetic core member 202, the coil 201 is wound as shown in FIG. 1.
When a current corresponding to an information signal is supplied to the coil 201, the magnetic head 200 generates a magnetically modulated vertical magnetic field from a distal end portion 205a of the magnetic core 205 on which the coil 201. is wound. In the magnetic head 200, the distal end portion 205a of the magnetic core 205 is cause to closely contact or slide in contact with the magneto-optical recording medium, and the vertical magnetic field generated from the distal end portion 205a of the magnetic core 205 is applied to the recording film of the magneto-optical recording medium, thus writing the information signal to the magneto-optical recording medium.
For a magneto-optical recording medium, a recording/reproducing device for the purpose of recording and reproducing music data is practically used. With such a recording/reproducing device for carrying out recording and reproduction on a magneto-optical disc, though a sufficient transfer rate is achieved in the case of recording and reproducing ordinary music data, a higher transfer rate is desired in the case of recording and reproducing image data in a computer or the like. As for music data, too, a higher transfer rate is desired in the case where duplication or shift is carried out.
To realize such a higher transfer rate, power saving and improvement in the magnetic field inversion band are made in the recording/reproducing device. Specifically, the inductance of the magnetic head 200 is reduced and miniaturization of the magnetic head 200 is done. Particularly, since the magnetic field is narrowed down and concentrated at the distal end portion 205a of the magnetic core 205, improvement in the generation efficiency of the magnetic field due to a so-called edge effect can be realized by narrowing the distal end portion 205a. 
In the magnetic head 200 shown in FIG. 1, narrowing the distal end portion 205a of the magnetic core 205 causes reduction in the cross-sectional area of the distal end portion 205a. Therefore, the range where an effective magnetic field is obtained is narrowed and it is difficult to carry out appropriate write operation onto the magneto-optical recording medium. That is, if the area of the distal end portion 205a of the magnetic core 205 is reduced, the intensity of an effective magnetic field applied to a predetermined recording track on the magneto-optical recording medium is insufficient for a positional deviation that is generated when an actuator for driving an objective lens within the recording/reproducing device into a focusing direction and a tracking direction makes a fine adjustment of the position of the objective lens, a positional deviation that is generated when the magneto-optical recording medium is loaded on the recording/reproducing device, and a positional deviation that is generated by the fluctuation of the magnetic head in the direction of height due to the wavering of the magneto-optical recording medium. Therefore, it is very difficult to carry out stable write operation of the information signal onto the magneto-optical recording medium.
If the distal end portion 205a of the magnetic core 205 is narrowed, the heat generated in the magnetic core member 202 concentrates at the magnetic core 205 and the magnetic core 205 is deteriorated by a high temperature. Therefore, a sufficient magnetic field cannot be generated.
Generally, in the magnetic head 200, when a current corresponding to an information signal is supplied to the coil 201, a magnetic field modulated by the information signal to be recorded is generated from the distal end portion 205a of the magnetic core 205 on which the coil 201 is wound. In this case, electric losses proportionate to the number of inversions of the magnetic field are generated. The electric losses mainly include a hysteresis loss due to the delay in the change of the direction of magnetization within the magnetic core member 202 from the change of the magnetic field by the coil 201, and an eddy-current loss due to the flow of an eddy current induced by the inversion of the magnetic field within the magnetic core member 202. All these losses are consumed as heat.
In the case where recording of music data is to be carried out as in the conventional technique, the calorific value due to the above-described electric losses is relatively small because of a low data transfer rate. Moreover, since the distal end portion. 205a of the magnetic core 205 has a large cross-sectional area and can efficiently release the generated heat toward the base 203 and the yokes 204a, 204b of the magnetic core member 202, the influence of such heating is not problematical.
However, in the case where the data transfer rate is high, the number of inversions of the external vertical magnetic field applied to the magneto-optical recording medium increases and therefore the calorific value due to the above-described electric losses increases, too. If the distal end portion 205a of the magnetic core 205 is narrowed, the generated heat cannot be efficiently released toward the base 203 and the yokes 204a, 204b of the magnetic core member 202 and the generated heat concentrates at the magnetic core 205, thus causing an abrupt increase in the temperature of the magnetic core 205. Moreover, in the magnetic head 200, it is often the case that a substantially cylindrical bobbin having the coil 201 wound on its outer circumferential surface is inserted in the magnetic core 205. If such a bobbin made of a synthetic resin or the like having a poor thermal conductivity is mounted on the outer circumferential surface of the magnetic core 205, the radiation property of the magnetic core 205 is deteriorated.
As a result, the temperature of the magnetic core 205 rises close to the Curie point and the magnetic core 205 becomes magnetically unstable. Therefore, appropriate write operation to the magneto-optical recording medium cannot be carried out. If the temperature rises to a point where the inductance is reduced, the current flowing through the coil 201 increases to generate thermal runaway, which may damage the magnetic head 200 or may damage a magnetic head unit or a recording/reproducing device using this magnetic head 200.
Thus, it is an object of the present invention to a magnetic head for supplying a magnetic field when recording an information signal onto a recording medium, and a magnetic head and a magneto-optical disc recording device used for recording on a recording medium, which enable solution of the above-described problem of the conventional magnetic head, restraint of magnetic deterioration due to heating, and realization of a higher transfer rate.
A magnetic head according to the present invention comprises: a substantially prism-shaped magnetic core portion having a distal end portion cut out to form a step, the magnetic core portion being form so that the cross-sectional area of the distal end portion is smaller than the cross-sectional area of a proximal end portion; and a coil wound on the outer circumferential surface of the magnetic core portion. The length of one side of the distal end portion is not less than 0.3 mm and not more than 0.45 mm, and the length of the other side orthogonal to the one side is not less than 0.4 mm and not more than 0.55 mm.
The height of the step formed at the distal end portion of the magnetic core portion is set to be not less than 0.3 mm and not more than a half of the length of the magnetic core portion.
Another magnetic head according to the present invention comprises: a core formed substantially in an E-shape by a substantially prism-shaped magnetic core portion having a distal end portion cut out to form a step, the magnetic core portion being form so that the cross-sectional area of the distal end portion is smaller than the cross-sectional area of a proximal end portion, and a pair of yokes arranged on both sides of the magnetic core portion; and a coil wound on the outer circumferential surface of the magnetic core portion and supplied with a current based on an information signal to be recorded onto a recording medium. The length of one side of the distal end portion of the magnetic core portion that is substantially parallel to the direction of movement of the recording medium is not less than 0.3 mm and not more than 0.45 mm, and the length of one side substantially orthogonal to the direction of movement of the recording medium is not less than 0.4 mm and not more than 0.55 mm.
A magneto-optical disc recording device according to the present invention comprises: an optical pickup unit arranged on the side of one surface of a magneto-optical disc and adapted for casing a condensed light beam to the magneto-optical disc; and a magnetic head arranged on the side of the other surface of the magneto-optical disc to face the optical pickup unit and adapted for applying an external magnetic field based on an information signal to be recorded onto the magneto-optical disc. The magnetic head used in this device has a core formed substantially in an E-shape by a substantially prism-shaped magnetic core portion having a distal end portion cut out to form a step, the magnetic core portion being formed so that the cross-sectional area of the distal end portion is smaller than the cross-sectional area of a proximal end portion, and a pair of yokes arranged on both sides of the magnetic core portion, and the magnetic head also has a coil wound on the outer circumferential surface of the magnetic core portion. The length of one side of the distal end portion substantially orthogonal to a recording track on the magneto-optical disc is not less than 0.3 mm and not more than 0.45 mm, and the length of one side substantially parallel to the recording track of the magneto-optical disc is not less than 0.4 mm and not more than 0.55 mm.
The other objects and specific advantages of the present invention will be further clarified by the following description of embodiments.